The present invention relates to a target device for use in a non-prism light wave range finder. In Particular, the invention is concerned with a target device comprising a base portion and at least one reflective surface formed on the base portion, with a colored reflective sheet as a retroreflective sheet being formed on the reflective surface.
A light wave range finder is generally an apparatus for indirectly measuring, with a light wave, a reflecting means installed in a target survey spot. A measuring light emitted from the light wave range finder is limited its output in terms of safety and electric power. Therefore, the reflecting means installed in the target survey spot is required to make an efficient reflection.
To meet this requirement, as reflecting means installed at the target survey spot there has been known a retroreflective means i.e., a corner-cube prism as a single prism and a reflective sheet configured by integrating micro-corner cube prisms. These reflecting means are configured so as to reflect incident light efficiently in the incident direction.
Recently, as a new light wave range finder, there has been developed a non-prism light wave range finder capable of measuring reflected light directly from a collimation target without using any reflecting means.
According to the configuration of such a non-prism light wave range finder, measuring light is emitted not continuously but as pulses. A laser diode (LD) is used as a light source which can emit a pulse light of a large output. Consideration is given also to safety and the power consumption is at a practical level.
In the non-prism light wave range finder, because of a large pulse output, the measurement of distance can be done even without using a reflecting means. Further, the use of a reflecting member will permit measurement of an extremely long distance.
In the non-prism light wave range finder, a measuring pulse light is emitted toward a target survey object such as a wall, then reflected light reflected directly from the target survey object is received, and the received signal is subjected to a signal processing and a numerical processing, thus permitting non-prism measurement.
The measuring light emitted from the non-prism light wave range finder is basically a collimated light and, for allowing the measuring light to reach a remote spot while suppressing its spread, it is emitted from the whole surface of an objective lens. Thus, the size of the measuring light is at least equal to the size of the objective lens and becomes wider as the distance increases. Such a measuring light is advantageous to the measurement of a uniform plane (for example, measurement of a natural object). Even if a plane to be measured has a certain degree of unevenness, it is possible to effect a uniform measurement.
In the case where the object of measurement is a lattice-like object, there arises the problem that reflected light from the lattice and reflected light from the background add together, making the measurement impossible. Where the background is near, it is possible to regard a midway distance as a centroid position and make measurement, but in case of measuring a road or the like there arises a serious problem that a measuring light irradiated surface tilts, and if there is included a strongly reflecting portion therein, a collimation center and the centroid position as the measurement center are very likely to be displaced from each other. This problem occurs unless the measurement is a true spot measurement.
The present invention relates to a target device for use in a non-prism light wave range finder. In Particular, the present invention aims at providing a target device comprising a base portion and at least one reflective surface formed on the base portion, with a colored reflective sheet as a retroreflective sheet being formed on the reflective surface. The reflective sheet as a retroreflective sheet formed on the reflective surface is colored.